1. Field of the Invention
The present invention relates to a technology for controlling light intensity of a light source when a fundus image is observed or taken.
2. Description of the Related Art
Conventionally, there has been known an ophethalmologic photographing apparatus configured as follows. A fundus of an eye to be inspected is irradiated by observation light that is steady light. A fundus image under the observation light, which is obtained by receiving reflected light from the fundus, is aligned while being observed. After that, photographing light, which is pulsed light, is projected so as to obtain a fundus image under the photographing light as a still image. The light reflectance of the fundus is different among individual eyes to be inspected, due to individual variation, lesion or the like. Therefore, it is necessary to provide a technology for appropriately controlling light intensity of the photographing light to be received by the photographing element.
As an example of such a technology, Japanese Patent Application Laid-Open No. H04-150831 discloses a technology of irradiating an eye to be inspected with the observation light and determining the light intensity of the photographing light based on the observation light reflected by the fundus.
However, in the technology disclosed in Japanese Patent Application Laid-Open No. H04-150831, light intensity control is performed only for a photographing light source. In the ophethalmologic photographing apparatus, it is also necessary to control the light intensity of the observation light when the fundus is observed under the observation light. However, in the technology disclosed in Japanese Patent Application Laid-Open No. H04-150831, it is necessary for an operator to appropriately adjust the light intensity of the observation light source manually while observing and aligning the fundus image in fundus observation.
In addition, the technology disclosed in Japanese Patent Application Laid-Open No. H04-150831 is aimed at taking a fundus image with appropriate light intensity. However, the appropriate light intensity in the fundus photographing varies due to various factors including the purpose of photographing, taste of a reader of the fundus image. The technology disclosed in Japanese Patent Application Laid-Open No. H04-150831 cannot perform the light intensity control flexibly to meet such a necessity. The same is true for observation light intensity. As to brightness of the fundus image to be observed, for example, if the fundus image is darker, it is usually easier to view an alignment index projected to the eye to be inspected for alignment, resulting in easier operation. Therefore, it is necessary to decrease the observation light intensity. However, on the contrary, when the fundus image is observed under the observation light, it is considered that the observation of the fundus image is easier under higher intensity of light. Therefore, it is necessary for the appropriate value of fundus image exposure to be set flexibly even in the case where automatic control of observation light intensity is performed.